What should I do if the 5100 error code appears after a software update?

If the 5100 error code appears after a software update, it's likely that the update introduced a bug or incompatibility. Try reverting to the previous firmware version if possible (consult Canon support for instructions). If reverting isn't an option, you may need to contact Canon support to report the issue and request a fix. It's also possible the update itself caused the issue; a factory reset might help.